High vacuum systems are widely used in technical and commercial applications such as semiconductor device manufacturing processes, which require the performance of the particular process in the absence of air and airborne contaminants. An example of such a process is the sputter deposition of thin films onto silicon wafer substrates in the manufacture of integrated circuit chips.
In such applications, the high vacuum sputtering system is typically composed of a metal processing chamber, which contains a variety of flanges or ports for the attachment of components such as vacuum producing pumps, sputtering cathodes, measurement instrumentation, access covers and observation windows. Additionally, specific ports are usually provided for the frequent insertion and removal of the wafer or other object being processed.
In order to provide a seal between members which is vacuum tight and yet removable for access or for component maintenance, the most commonly used device is a commercially available elastomeric gasket known as an O-ring. The material of choice for such seals is a rubber-like fluorocarbon material manufactured by E. I. Dupont de Nemours Inc. under the trademark VITON A. This material combines the desirable properties of low out-gassing, low permeability and good compressibility over a useful temperature range.
Most components attached with elastomeric seals are removed infrequently. However, seal ports used for the insertion and removal of objects being processed may be opened and closed as frequently as twice per minute, for 24 hours per day. This type of use generates microscopic particles of both seal material and of adjacent metal surfaces. Such particles are of extreme concern as they can destroy integrated circuits or other devices on the substrate being processed, thus causing a costly reduction in manufacturing yield.
For example, in the case of frequently cycled sealing ports, where a transfer chamber is provided and maintained at a high vacuum of 10.sup.-7 torr, each time a substrate passes through a sealing port, that port is opened and then closed to isolate the environments between adjacent chambers, such as process chambers, a transfer chamber or load chambers.
The slit valve seal plate contains a sealing O-ring. The O-ring is totally compressed to provide a reliable vacuum seal against standard atmospheric pressure in the order of 14.7 pounds per square inch or 760 Torr, which is a pressure differential experienced between a transfer chamber and a loadlock chamber, or between a transfer chamber and a processing chamber when the processing chamber is occasionally opened to atmosphere for service. O-ring seals are also similarly compressed each time a wafer is transferred therethrough in the systems of the prior art when the pressure differential between adjacent chambers is significantly less than 760 Torr.
This compression of an O-ring produces microscopic particles which can be highly deleterious to the product being produced. These particles are produced in two ways. Firstly, repeated compression of the O-ring to the degree necessary to form a reliable standard atmospheric pressure tends to fatigue the elastomer material of which the O-ring is made, causing minute failures which generate elastomer particles. Secondly, as the O-ring is compressed into groove, sliding friction occurs along side faces of groove. This friction abrades both the surface of the O-ring and side surfaces of the groove, producing particles of both elastomer and metal. This abrasion also occurs during decompression of the O-ring.
The presence of such particles in processes such as the manufacture of semiconductor devices results in a substantial loss of value and productivity. This is increasingly the case with the trend toward device miniaturization in which the presence of a sub-micron size particle on the surface of a substrate can result in the production of a totally defective device.
Accordingly, there is an increased need to reduce the quantity of contaminating particles in high vacuum processes, particularly in the manufacture of semiconductor devices.